1. Field of the Invention
The present invention relates to a cathodic protection test station. More particularly, the present invention relates to a cathodic protection test station having a removable housing which locks onto a base plate and also having displacable wedge members formed on the base plate for securing the test station to a tube.
2. Prior Art
Underground metallic structures, such as pipelines, are subject to corrosion. These structures are expensive and difficult to construct and perhaps more difficult and expensive to repair or replace due to corrosive failure. In addition, some structures serve vital functions where catastrophic failure of the structure may result in more harm than the mere loss of the structure itself. For example, a pipeline may contain toxic or volatile liquids and gases whose escape through a corrosion failure in the pipeline can endanger lives and the environment.
Corrosion is the dissolution of a metal into an aqueous environment. The metal atoms dissolve as ions. Electro-chemical, or aqueous, corrosion occurs when a metal in an aqueous solution loses material to the solution. The variation in the metal ion concentrations in the solution causes an electrical current through the metal. The corroding metal acts as an anode and supplies electrons. This is known as an anodic reaction. Galvanic corrosion occurs when a more active metal is in contact with a more noble metal in an aqueous solution. The more active metal loses electrons to the more noble metal. The non-corroding metal acts as a cathode and receives electrons. This is known as a cathodic reaction.
Numerous methods have been developed to prevent corrosion. The most obvious method would be to coat the metallic structure with a non-corrosive coating, such as plastic or ceramic. Coating the structure, however, can be impracticable and expensive due to the enormous size of the structure.
A less obvious method for preventing corrosion, and the method which has garnered wide spread acceptance, involves manipulating the electro-chemical and galvanic phenomena involved in the corrosion itself; otherwise known as cathodic protection. Cathodic protection involves applying protective electrical currents from a more easily corroded metal such as magnesium or zinc. An electrical circuit is set up so that the magnesium or zinc corrodes as a sacrificial anode while the less active metal serves as the cathode and is not affected. This effect can also be obtained from an external source through a graphite or platinum anode receiving current from a rectifier, generator, or battery. Under both these conditions, current flows from the external anode through the soil to the structure. This current is of sufficient magnitude to afford cathodic protection to the underground structure.
The circuit that is established must be monitored to maintain optimum performance. This is achieved through the use of a variety of monitoring instruments. The instrument's primary function is to measure structure or pipe to soil potentials, i.e. the relative voltage in the circuit. If a major fluctuation occurs in this circuit, the structure may begin to corrode and an adjustment is necessary to compensate.
The underground location of the structure presents a special problem in that several feet of earth separate the structure from inspection. To monitor these voltage potentials, a test station is used. The test station is a passive device connected to the underground structure that offers a contact point in which the instrument can be connected to obtain the readings. The connection is usually made by means of a coated wire that is chemically welded to the structure. The wire is brought above ground through a conduit capped off with a condulet. The condulet or test station, will have connections to the wire.
The test station is positioned at any point of the structure where it is desired to monitor the voltage potential. In a pipeline application, numerous test stations are established along the length of the pipe.
The conduits may be metal or plastic, flexible or rigid. Although metal is widely used, it presents an electrical shock hazard and must be painted or coated to prevent corrosion. Plastic conduit is becoming more popular. Many test stations are actually a test station and conduit combination with the station and the conduit having a special fitting for joining them together. The problem with this configuration is that the station must be used with its mating conduit which adds cost and complexity to the installation of the station. In addition, the conduit is often of a nonstandard size and shape; making it more expensive that readily available, standard pipe, conduit and tubing.
An addition problem facing test stations is their location outdoors and in remote locations. The test stations are subject to adverse weather conditions and potential abuse by vandals.
Therefore, it would be advantageous to develop a cathodic test station capable of being used with standard pipe, conduit, and tubing. It would also be advantageous to develop a cathodic test station that is quickly and easily installed. Furthermore, it would be advantageous to develop a cathodic test station capable of resisting vandalism and adverse weather conditions.